1. Field of the Invention
The present invention relates to military applications of signal processing related to radar and communication recorded and simulated signals.
2. Description of the Related Art
Since the use of radio detection and ranging (hereinafter referred to as radar) during World War II, signal processing has been required to analyze signal returns which were reflected from targets. Signal processing is performed on the reflected target returns and a reference of the original transmitted signals. Currently, radar systems and their signal processors must be tested in hardware-in-the-loop (HIL) studies using simulated targets and recorded returns from flight tests as well as during mission flight tests on real targets. Mission flight tests typically cost approximately 25 million dollars to conduct and HIL studies using mission flight test data are limited to using the radar waveforms that were used during the mission flight test. Mission flight test data has been taken since the 1960s and exists on computer data tapes. As new radars are developed costly and repetitive mission flight tests must be conducted to test the new radars, their advanced transmitted waveform repertoire, and their advanced signal processing capability. With the large volume of recorded mission flight test data, a logical motivation is to reconstruct these recorded data into formats that can be convolved with any advanced reference waveform so that these recorded and costly to gather mission flight test data could serve to test new advanced waveforms and signal processors. Currently there is no way to reconstruct these data into radio frequency returns which can be referenced to the non-linear frequency modulated (LFM) waveforms sampled at different bandwidths and different operating frequencies that were used to gather the recorded mission flight test data.
The related art is represented by the following patents of interest.
U.S. Statutory Invention Registration Number H481, issued on Jun. 1, 1988 to Francis X. Filardo et al., describes a microprocessor-controlled RF modulator apparatus which is controllable in both attenuation range and frequency. Filardo et al. do not suggest a down range returns simulator according to the claimed invention.
U.S. Pat. No. 3,903,521, issued on Sep. 2, 1975 to Garold K. Jensen et al., describes a signal simulator which will produce video signals suitable for driving an acceleration gate radar system in a manner of operation likely to be encountered with actual return signals from ballistic missiles and the like. Jensen et al. do not suggest a down range returns simulator according to the claimed invention.
U.S. Pat. No. 4,005,424, issued on Jan. 25, 1977 to Richard W. Fetter, describes a waveform generator particularly suited for the simulation of Doppler radar returns from precipitation. Fetter does not suggest a down range returns simulator according to the claimed invention.
U.S. Pat. No. 4,168,502, issued on Sep. 18, 1979 to William F. Susie, describes a target signal simulator for generating a simulated target signal useful in testing the receiver and data processing portions of radar systems that includes means for accepting a synchronizing signal having a PRF and duty cycle substantially equal to the PRF and duty cycle of the transmitter utilized by the radar system to be tested. Susie does not suggest a down range returns simulator according to the claimed invention.
U.S. Pat. No. 4,450,447, issued on May 22, 1984 to Howard A. Zebker et al., describes a synthetic aperture radar target simulator for altering the frequency and delay of an input rf signal by an amount related to range curvature information and Doppler frequency information associated with a simulated target. Zebker et al. do not suggest a down range returns simulator according to the claimed invention.
U.S. Pat. No. 4,625,209, issued on Nov. 25, 1986 to Gene W. Lawrence et al., describes a terrain return (clutter) generator for use in radar evaluation. Lawrence et al. do not suggest a down range returns simulator according to the claimed invention.
U.S. Pat. No. 4,665,403, issued on May 12, 1987 to Kurt 0. Edvardsson, describes method and apparatus for measuring the distance from an antenna to the surface of a fluent material such as a liquid or a particulate solid material with the use of a microwave signal, the frequency of which varies substantially linearly during a measuring interval and one part of which is emitted from the antenna towards the surface to be reflected therefrom and, after a propagation time corresponding to the sought distance, to be received and mixed with the signal which has been emitted at that instant, so that a measuring signal with a measurement frequency dependent upon the distance is obtained. Edvardsson does not suggest a down range returns simulator according to the claimed invention.
U.S. Pat. No. 5,039,991, issued on Aug. 13, 1991 to Otto A. Boese et al., describes a system for receiving electromagnetic radiation, which may be subject to environmental perturbations, and producing a system output that is substantially unaffected by the perturbations. Boese et al. do not suggest a down range returns simulator according to the claimed invention.
U.S. Pat. No. 5,133,663, issued on Jul. 28, 1992 to Joseph A. Willingham et al., describes a portable automatic radar simulator which when connected to a transmitting means such as a magnetron generated microwave threat transmitter will simulate up to 2048 preprogrammed radar signature. Willingham et al. do not suggest a down range returns simulator according to the claimed invention.
U.S. Pat. No. 5,134,412, issued on Jul. 28, 1992 to Behshad Baseghi et al., describes an apparatus for simulating a signal received by a radar system in response to RF energy transmitted by an emitter. Baseghi et al. do not suggest a down range returns simulator according to the claimed invention.
U.S. Pat. No. 5,247,843, issued on Sep. 28, 1993 to Richard H. Bryan, describes a method and apparatus for using compact ranges to simulate electromagnetic environments for computer-driven test systems utilizing but not expending performance hardware. Bryan does not suggest a down range returns simulator according to the claimed invention.
U.S. Pat. No. 5,457,463, issued on Oct. 10, 1995 to Leslie J. Vencel et al., describes a radar return signal generator apparatus for generating one or more radar return signals representative of one or more remote objects useable in ground based, shipboard and airborne radar systems for testing radar and its user. Vencel et al. do not suggest a down range returns simulator according to the claimed invention.
U.S. Pat. No. 5,721,554, issued on Feb. 24, 1998 to Stanley R. Hall et al., describes a near field planar wavefront generation method that uses a relatively small number (three to five) of transmitting antennas to create a synthesized one-dimensional linear plane of radiation over 10 to 20 wavelengths at a specific location on an antenna array of a system under test at a specific frequency and distance, typically in the range of from 100 to 200 feet. Hall et al. do not suggest a down range returns simulator according to the claimed invention.
Germany Patent document 4,002,857, published on Sep. 19, 1991, describes a device for ascertaining the mean Doppler frequency of a synthetic aperture radar in real time by reading complex data in a buffer memory module as range lines and reading out as azimuth lines. Germany '857 does not suggest a down range returns simulator according to the claimed invention.
Great Britain Patent document 2,209,643 A, published on May 17, 1989, describes a pulse compression radar. Great Britain '643 does not suggest a down range returns simulator according to the claimed invention.
International Patent document WO88/08987, published on Nov. 17, 1988, describes a method for implementing the test in operation of a radar information display device such as a digital transformer for images. International '987 does not suggest a down range returns simulator according to the claimed invention.
International Patent document WO89/08854, published on Sep. 9, 1989, describes a radar test set target which is co-located with the radar and produces a faithful replica of the radar signal substantially delayed in time. International '854 does not suggest a down range returns simulator according to the claimed invention.
Japan Patent document 61-225678, published on Oct. 7, 1986, describes a pseudo target generator for pulse Doppler radar. Japan '678 does not suggest a down range returns simulator according to the claimed invention.
Japan Patent document 1-201180, published on Aug. 14, 1989, describes a dummy signal generating device for radar. Japan '180 does not suggest a down range returns simulator according to the claimed invention.
Japan Patent document 1-313785, published on Dec. 19, 1989, describes a radar simulator system. Japan '785 does not suggest a down range returns simulator according to the claimed invention.
Japan Patent document 2-183187, published on Jul. 17, 1990, describes a method and apparatus for generating a simulated object signal. Japan '187 does not suggest a down range returns simulator according to the claimed invention.
An article entitled "Simulators as Test Equipment and Training Devices for EW and Radar" by James B. Y. Tsui, published in September, 1989 on pages 38, 40, 42, 44, 46, 48, and 50 of the MICROWAVE JOURNAL, describes three different types of frequency channelizers according to their outputs. The Tsui article does not suggest a down range returns simulator according to the claimed invention.
An article entitled "Channelizers and Frequency Encoders", published in March, 1980 on pages 28, 30, 32, 38, 40, 42, 41, 70, and 71 of a magazine entitled Military Electronics/Countermeasures, describes a description of four systems for test and training purposes. The Military Electronics/Countermeasures article does not suggest a down range returns simulator according to the claimed invention.
An article entitled "A Target Simulator for Frequency Agile Radars" by John A. H. Wall, published in September, 1980 on pages 251-256 of a document entitled Conference: Proceedings of the 11th European Microwave Conference, describes a prototype radar target simulator possessing features essential for testing frequency-agile and coherent systems. The Wall article does not suggest a down range returns simulator according to the claimed invention.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed.